NCERT Gist: Microorganisms: Friend And Foe | Additional Study Material for UPSC PDF Download

- Living organisms which can’t been seen with eyes alone are called microorganisms or microbes.
- Microorganisms are classified into four major groups.
- These groups are bacteria, fungi, protozoa and some algae.
- Viruses are also microscopic.
- They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.
- Common ailments like cold, influenza (flu) and most coughs are caused by viruses.
- Serious diseases like polio and chicken pox are also caused by viruses.
- Diseases like dysentery and malaria are caused by protozoans whereas typhoid and tuberculosis (TB) are bacterial diseases.
- Microorganisms like amoeba can live alone, while fungi and bacteria may live in colonies.
- They are used in the preparation of curd, bread and cake.
- Microorganisms have been used for the production of alcohol since ages.
- Bacteria are also used in the preparation of medicines.
- In agriculture they are used to increase soil fertility by fixing nitrogen.
- Curd contains several microorganisms.
- Of these, the bacterium Lactobacillus promotes the formation of curd.
- It multiplies in milk and converts it into curd. Bacteria are also involved in the making of cheese, pickles and many other food items.
- An important ingredient of rava (sooji) idlis and bhaturas is curd.
- Yeast reproduces rapidly and produces carbon dioxide during respiration.
- Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar).
- Yeast is used for commercial production of alcohol and wine.
- For this purpose yeast is grown on natural sugars present in grains like barley, wheat, rice and crushed fruit juices, etc. process of conversion of sugar into alcohol is known as fermentation.
- Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.
- Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.
- Polio drops given to children are actually a vaccine.
- Some bacteria and blue green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility.
- These microbes are commonly called biological nitrogen fixers.
- The microorganisms decompose dead organic waste of plants and animals converting them into simple substances.
- These substances are again used by other plants and animals.
- Thus, microorganisms can be used to degrade the harmful and smelly substances and thereby clean up the environment.
- Some of the microorganisms cause diseases in human beings, plants and animals.
- Such disease-causing microorganisms are called pathogens.
- Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases.
- Examples of such diseases include cholera, common cold, chicken pox and tuberculosis.
- There are some insects and animals which act as carriers of disease causing microbes.
- Housefly is one such carrier.
- Anopheles mosquito , which carries the parasite of malaria.
- Female Aedes mosquito acts as carrier of dengue virus.
- Anthrax is a dangerous human and cattle disease caused by a bacterium.
- Foot and mouth disease of cattle is caused by a virus.
- Salts and edible oils are the common chemicals generally used to check the growth of microorganisms.
- Therefore they are called preservatives.
- Sodium benzoate and sodium meta bisulphite are common preservatives.
- These are also used in the jams and squashes to check their spoilage.
- Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.
- Pasteurized milk can be consumed without boiling as it is free from harmful microbes.
- The milk is heated to about 70 degree C for 15 to 30 seconds and then suddenly chilled and stored.
- By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called pasteurization.
- Rhizobium lives in the root nodules of leguminous plants, such as beans and peas, with which it has a symbiotic relationship.
- Some microorganisms reside in the root nodules of leguminous plants.
- They can fix nitrogen from air into soil and increase the soil fertility.
- Some bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into nitrogenous compounds.
- Certain bacteria convert compounds of nitrogen present in the soil into nitrogen gas which is released to the atmosphere.